Polyimides are a class of polymers that have proved useful in aeronautical and space applications through molding, calendering and injection molding. Linear aromatic polyimides, although not processable via conventional thermoplastic or hot-melt techniques, are exceptionally thermally stable, have a high glass transition temperature, and are resistant to attack by common organic solvents. Linear aromatic polyphenylene oxides and sulfides, on the other hand, are more easily processed than polyimides, exhibit lower glass transition temperatures, have good thermal stability although not equal to polyimides, and do not have the solvent resistance of polyimides. In the present invention a novel polymer has been synthesized that combines the favorable properties of both polyimides and polyphenylene oxides and sulfides. The new system can now be processed using conventional thermoplastic techniques. In order to maximize use properties and processability, molecular weight was varied by varying the amount of endcapping with a monoanhydride. The effect of endcapping is to decrease both molecular weight and apparent viscosity, the latter decreasing by two orders or magnitude at a processing temperature of 250.degree. C. and three orders of magnitude at a processing temperature of 280.degree. C.
Accordingly, an object of the present invention is to provide a process for making a polyimide that is processable via conventional thermoplastic or hot-melt techniques.
Another object of the present invention is to provide a process for endcapping a polyimide system with a monoanhydride.
Another object of the present invention is to provide a process for controlling molecular weight and apparent viscosity of a polyimide at different temperatures.
A further object of the invention is to maximize flow characteristics for a molecular weight material with the desired fracture resistance by establishing the relationship between the amount of endcapping, molecular weight, and fracture resistance.